Indexing depends on multiple factors, including the quality of the website, content on the page, DA, and more. If you have taken backlinks from websites where anyone can post links, it will take time to index, if not indexed at all. Because people usually go there just to get backlinks, for example, directory sites or Web 2.0 sites as mentioned by
@Titans.
In order to get quality backlinks, you should contact quality websites for guest posts or ask relevant website owners to recommend you on their site (not in the spammy/black hat way). These kinds of backlinks will surely take a lot of time and effort but will surely get indexed fast and give you good benefits.